The present invention relates to a method for reducing noxious or toxic exhaust emissions from an internal combustion engine, particularly those emissions which are generated immediately after starting the engine from cold.
In many countries, legislation dictates a permitted maximum level of exhaust gas emissions from vehicle engines. Typically, catalytic converters are employed to remove or reduce the levels of certain noxious or toxic emissions from exhaust gases. However, catalytic converters become efficient only once they reach their light-off temperature and therefore do not immediately contribute to a reduction of cold-start emissions. Conventional fuel delivery systems for internal combustion engines employ an exhaust gas oxygen sensor, commonly termed a lambda sensor, to determine the amount of oxygen in the exhaust gases and to adjust the amount of fuel delivered to the cylinders of the engine based on the value of the signal generated by the sensor. As with a catalytic converter, however, a lambda sensor can only begin to operate once it has reached a particular operating temperature.
It is during the period from cold-starting an engine until its catalytic converter reaches its light-off temperature that the vast majority of undesirable exhaust emissions is discharged to the atmosphere. Much research relating to the reduction of cold-start emissions from internal combustion engines is documented in patent literature. For example, in an attempt to compensate for the lack of a lambda sensor control signal during start-up from cold, it is proposed in WO-A-89/04917 to provide an engine control device in which a first datablock is programmed for operation in accordance with certain engine operating parameters but without lambda control when the engine is cold. A second datablock is programmed for operation with lambda control when the engine is warm. Switching logic switches in the first datablock when the engine is started below a lower threshold temperature and switches over to the second datablock when the temperature rises above a higher threshold temperature.
Due to variations in fuel quality, an engine is typically given a rich air-fuel mixture when being started and when running cold to ensure that smooth running of the engine is achieved without risk of the engine stalling. It is known from EP-A-0 807 751 to provide an engine with an after-start lean-burn control. To achieve smooth running of the engine when the after-start lean-burn control is switched in, the idling rotational speed of the engine is increased. EP-A-0 807 751 further proposes idling control apparatus which compensates for changes in engine torque as the after-start lean-burn control is switched in and out.
In GB-A-2 316 197, various problems associated with variations in fuel blends are identified. In order to operate an internal combustion engine smoothly during start-up and cold idling regardless of the fuel quality, it is proposed in that document to measure the rotational speed of the engine crankshaft and compare the measured speed with an expected engine speed. A speed error is then calculated and the amount of fuel delivered to be combusted in each of the cylinders is adjusted to reduce the speed error.
Although the arrangements discussed above may provide improved running characteristics for engines operating when cold, there still exists a need for cleaner exhaust gases when starting an engine from cold.
The present invention in its several disclosed embodiments alleviates the drawbacks described above with respect to conventionally designed methods for reducing cold-start emissions from internal combustion engine and incorporates additionally beneficial features.
In this regard, it is an object of the present invention to provide a method of reducing noxious or toxic exhaust emissions from an internal combustion engine without noticeably affecting smooth running of the engine. This objective is achieved in accordance with the present invention by reducing noxious or toxic exhaust emissions from an internal combustion engine. The engine has a plurality of cylinders that cooperate with a crankshaft to cause the crankshaft to rotate at a rotational speed when said cylinders are provided with an air/fuel mixture having a lambda value. The mixture is ignited to generate pressure in the cylinders. The method includes measuring a parameter reflecting the pressure in a first cylinder during at least a part of a working stroke of that first cylinder when supplied with an air/fuel mixture having a first lambda value to thereby obtain a first parametric value. An air/fuel mixture is provided to a second cylinder that has a second lambda value which is different from the first lambda value and which causes the second cylinder to perform a working stroke. A parameter is measured reflecting the pressure in the second cylinder during at least a part of the working stroke of the second cylinder to obtain a second parametric value. The first and second parametric values are compared to obtain a parametric comparison value. The lambda value is adjusted for the air/fuel mixture to a subsequent cylinder dependent on the parametric comparison value.
In one particularly advantageous embodiment of the invention, the parameter reflecting the pressure in the first cylinder is a first rotational acceleration value determined by measuring the rotational speed of the crankshaft at two instances during at least a part of the working stroke of the first cylinder. The parameter that reflects the pressure in the second cylinder is a second rotational acceleration value determined by measuring the rotational speed of the crankshaft at two instances during at least a part of the working stroke of the second cylinder. The parametric comparison value is a rotational acceleration comparison value attained by comparing the first rotational acceleration value with the second rotational acceleration value.
The method in accordance with the present invention can be utilized as soon as the engine is started; that is, during the first cycle. Since the method causes the engine to more quickly adopt a leaner mixture, a considerable reduction of hydrocarbon emissions is attained, as is a reduction in fuel consumption. Because the principle underlying the invention is based on a relative comparison of the different combustions, the method is insensitive to variations due to wear during the life of an engine, as well as being independent of external factors such as fuel, temperature, altitude, and the like.
The beneficial effects described above apply generally to the exemplary devices, mechanisms and methods disclosed herein for the present invention. The specific structures through which these benefits are delivered will be described in detail hereinbelow.